1. Field of the Invention
The present invention relates to a magnetoresistance element for detecting a variation of magnetic field and particularly relates to a magnetic detection element which is provided with a giant magnetoresistance element with high level output, method of production of it and magnetic detection device.
2. Description of the Prior Art
Generally speaking, a magnetoresistance element (hereinafter relate to MR element) is an element whose resistance value changes depending on an angle between a magnetization direction of a thin film consisting of a ferromagnetic substance (e.g. Ni--Fe, Ni--Co, etc.) and a direction of electric current.
Resistance of the MR element as above takes a minimum value when an electric current direction and magnetization direction intersects at right angle and takes a maximum value when angle between electric current direction and magnetization direction becomes zero: i.e., both of directions are the same or reversed each other completely. Such a change of resistance value is referred to MR change rate and generally Ni--Fe and Ni--Co takes a rate of 2.about.3% and 5.about.6% respectively.
FIG. 9 and FIG. 10 are a side view and a perspective view respectively showing a structure of a conventional magnetic detection device.
As shown by FIG. 9, a conventional magnetic detection device is provided with a rotation shaft 41, a disk shaped magnetic rotating body having at least one or more of uneven face of recess and protrusion on its periphery and rotating synchronously with a rotation of the rotation shaft 41, a MR element 43 which is arranged with a gap having a predetermined distance with the periphery of the rotating body, a magnet 44 fixed to the back side of the MR element 43 for supplying a magnetic field to the MR element 43 and an integrated circuit 45 for processing an output of the MR element 43; and the MR element 43 consists of a magnetic resistance pattern 46 and a thin film surface 47(magnetosensitive surface).
In the foregoing magnetic detection device, the magnetic field penetrating through to thin film surface 47, i.e. a magnetosensitive surface of the MR element 43 changes due to the rotation of the magnetic body 42, thereby the resistance value of the magnetic pattern 46 changes.
However, the output level of the MR element 43 used for the magnetic detection device as above is low and therefor a detection with high accuracy can not be performed. In order to overcome this problem, recently a magnetic detection element employing a giant magnetoresistance element (hereinafter refer to as GMR element) with a high level output has been proposed.
FIG. 11 shows characteristics of a conventional GMR element.
The GMR element exhibiting the characteristics shown by FIG. 11 is a laminated layers member acting as so called an artificial lattice membrane arranged in lamination of an alternate succession of a magnetic layer having a thickness of several .ANG. to several tens .ANG. and a non magnetic layer (Fe/Cr, and permalloy/Cu/Co/Cu, Co/Cu, FeCo/Cu) which is disclosed by an article bearing a title of "magnetoresistance effect of an artificial lattice" appearing in Journal of Japanese Applied Magnetism, Vol.15, No,51991, pp.813.about.821. This laminated member has an extraordinarily high MR effect (MR change rate) comparing with the MR element as mentioned above and also is possible to obtain the same change of resistance regardless of direction of external magnetic field with respect to electric current.
In order to detect a change of magnetic field, carrying out formation of a substantial magnetosensitive surface using a GMR element, formation of electrode on each end of the magnetosensitive surface and forming a bridge circuit between these ends, connecting a power supply for a constant voltage and a constant current between two electrodes facing each other, and converting change of resistance value of the GMR element to change of voltage and then it is possible to arrange the detection of change of magnetic field being acted on the GMR element.
FIG. 12 and FIG. 13 are a side view and a perspective view, respectively, of a structure of a magnetic detection device using a conventional GMR element.
FIG. 12 and FIG. 13, this magnetic detection device comprises a rotation shaft 41, a disk shaped magnetic rotating body as a means of providing a magnetic field change due to a rotating magnetic field synchronously with the rotation of the rotating shaft 41 and having at least one uneven surface of recess and protrusion on that rotating body, a GMR element 48 which is arranged with a gap of predetermined spacing facing the outer periphery of the magnetic rotating body 42, a magnet 44 as a means for providing a magnetic field to the GMR element 48 and an integrated circuit 45 for processing output of the GMR element 48; and the GMR element 48 has a magnetic resistance pattern 49 as a magnetosensitive pattern and a thin film surface 50.
In the magnetic detection device as above, a magnetic field penetrating through the thin film surface (magnetosensitive surface) 50 of the GMR element 48 changes due to rotation of the magnetic rotating body 42, thereby resistance value of the magnetoresistance pattern 49 changes.
FIG. 14 is a black diagram of a magnetic detection device employing a conventional GMR element, and FIG. 15 is a detailed block diagram of a magnetic detection device employing a conventional GMR element.
A magnetic detection device shown by FIG. 14 and FIG. 15 comprises a Wheatstone bridge circuit using a GMR element 48 which is arranged with a gap having a predetermined distance with a magnetic rotating body 42 and is supplied with a magnetic field from the magnet 44, a differential amplifier circuit 52 for amplifying an output of the Wheatstone bridge circuit 51, a comparator circuit 53 for outputting "0" or "1" signal by comparing this output value of the differential amplifying circuit 52 with a reference value and an output circuit 54 for performing switching upon reception of the output of the comparator circuit 53.
FIG. 16 shows an example of a circuit arrangement of a magnetic detection device using a conventional GMR element.
FIG. 16, a Wheatstone bridge circuit 51 has, for example, the GMR element 48a, 48b, 48c, and 48d on each side of it; and the GMR element 48a and GMR element 48c are connected to the power supply terminal VCC, the GMR element 48b and the GMR element 48d are grounded, each of the other end of the GMR element 48a and that of the GMR element 48b is connected to a connection point 55 and each of the other and of the GMR element 48c and the GMR element 48d is connected to a connection point 56.
The connection point 55 of the Wheatstone bridge circuit 51 is connected to an inverse input terminal of the amplifier 59 of the differential amplifier circuit 58 through a resistor 57, and the connection point 56 is connected to a non-inverse input terminal of the amplifier 59 through a resistor 60 and further connected to a potential dividing circuit 62 which provides a reference voltage on the basis of the voltage supplied from the power supply terminal VCC.
An output terminal of the amplifier 59 is connected to it's own inverse terminal through a resistor 63 and also is connected to an inverse input terminal of the amplifier 65 of the comparator circuit 64; and a non-inverse input terminal of the amplifier 65 is connected to a potential dividing circuit 66 which provides a reference voltage on the basis of the voltage supplied from the power supply terminal VCC and also is connected to an output terminal of an amplifier 65 through an resister 67.
An output end of the comparator circuit 64 is connected to base of a transistor 69 of the output circuit 68, collector of the transistor 69 is connected to an output terminal 70 of the output circuit 68 and is connected also to the power supply terminal VCC through a resistor 71 and the emitter of this transistor is grounded.
FIG. 17 shows a structure of a conventional magnetic detection element and FIG. 18 shows an operational characteristics of a conventional magnetic detection element.
As shown by FIG. 17, the Wheatstone bridge comprises a GMR element 48 (consisting of 48a.about.48d) As shown by FIG. 18, as the magnetic rotating body 42 rotates, the magnetic field supplied to the GMR element 48 (48a to 48d) changes and as shown by FIG. 18 an output corresponding to the uneven surface of recess and protrusion of the rotating body 42 can be obtained at the output end of the differential amplifier circuit 58.
This output of the differential amplifier circuit 58 is supplied to the comparator (circuit 64, compared with a reference value, a level to be compared, and converted to a signal of "0" or "1" and this converted signal is further waveform shaped by the output circuit 68 and as a result, signal of "0" or "1" with a sharp rise or fall can be obtained at the output terminal 70 of it as shown by FIG. 18.
Characteristics of the GMR element used for the foregoing magnetic detection element includes, however a hysteresis with respect to applied magnetic field, and this causes reduction of sensitivity when a range of magnetic field set by the magnetic detection device is narrow, and as a result there may be a possibility that practice of detection will encounter difficulties. Since the magnetic characteristics of the GMR element is temperature dependent similar to metal films in general, there may also arise a likelihood of troubles in practice of detection when temperature in operation rises even when the element has sufficient sensitivity in the range of magnetic field set for the magnetic detection device at room temperature.
Therefore, there was a problem such that a possibility of not obtaining a sufficient output signal is expected in the case where a range of magnetic field is extremely small only in a particular portion as exemplified by partially narrowed spacing between a recess and protrusion of the rotating body facing the magnetic detection element.
Also there is problem such that, when an environmental temperature in operation is sever (e.g. higher than -40.degree. C. and lower than 15.degree. C.) as in a case of an automobile application, an output can not be obtained on a high temperature side. Now, for automobile application various way of usage of this element such as rotational speed detection of engine and wheel for engine control and brake control are considered.
Accordingly, the present invention is made in order to solve foregoing problems and object of this invention is to provide a magnetic field detection device having a wide environmental operational temperature range and high detection sensitivity